Vulcanization of caoutchouc



Patented Jan. 4, 1927. o

. UNITED STATES PATENT oFrlcEL CLAYTON w. RRDroRn, or AxRoN, OHIQQSSIGNOR TO run B. F. GoopRrdn comrm, on NEW YoRK, 11.1, A CORPORATION or new YoRK, Ann 'rnn eoonxnaR 'rmn RUBBER com ANY, or AKRQN, OHIO,

a CORPORATION or OHIQ. p

VULGANIZATION or oaov'ronouo.

No Drawing. Original application filed February 11, 1925, Seriai No; 8,548. Divided and this application I flied October 19, 1926. Serial No. 142,782.

This invention relates to the art of vulca'nizing rubber by the aid of a vulcanization accelerator and its chief object is to provide arr-improved method of vulcanizing rubber whereby premature vulcanization or scorching of the rubber compound, such as often results from incorporating powerful or low temperature accelerators with the rubber on the mixing-mill, may be conveniently avoided without sacrificing curing power of the accelerator.

The present application is adivisiori of vmy copending application Serial No. 8,543, filed February 11., 1925, which relates to the same field of invention as the disclosures in my co-pending applications. Serial No. 683,233. filed December 28, 1923, and Serial No. 616,220. filed January 31, 1923, and to the extent that this application contains subject-matter in common with the abovementioned applications. it may be considered as'a continuation thereof.

Zinc dithiocarbamates and zinc mercaptides are known tothe art as powerful accelerators of vulcanization. They are characterized by rapid curing power even at ordinary temperatures and much trouble is experienced with scorching or curing on the mills or calenclers. These difficulties are so avoided to a certain extent by the use of low temperatures during processing, use of low sulfur content or low accelerator content in the rubber mix or by such methods as mixing the sulfur and accelerator into separate portions of rubber, such master vbatches being mixed just before use or built up in alternate calendered plies. These methods diminish the production from a given equip- 'ment of mills and calenders, decrease the output of paratus, or necessitate greatly increase labor costs.

tetrainethyl thiuram disulfide or Disulfides having doublebond in such I takes place in about one week. Before treatnot cure wa rou as x g P of which mercaptobenzothiazol disulfide are illustra .tive, are also known to the art as powerful .in acceleration,

a iven equipment of curing apb d peratures in three months,

ment with ammonia gas until saturated and .in hot airin .50 minutesat 80 after treatment an oven-cure is obtained under the 'same, conditions A accelerators, but are characterized as functioning at substantially higher temperatures than, the corresponding zinc .salts.

Being therefore comparatively free from scorching and air curing they are in many instances preferred'to the zinc' dithiocarbamates and zinc mercaptides even though they. show a lower degree of acceleration.

I have now found a method of transforming the disulfides into the corresponding zinc salts, with the resultant increase.

after the incorporation of such disulfides into the rubber inix and subsequent to all factory manipulations wherein, I

scorching or air curingare undesirable.

This process s accomplished by mixing and calendering or otherwise manipulating a.- mixture of rubber, metallic oxide, sulfur,

disulfide and other compounding '1ngred1-" ents, if desired, to. form the unvulcanized stock into approximately the final shape of the vulcanized product.- The unvulcanized J article is then treated with ammonia, or an organic amine, preferably by submitting such articles to the vapors of the nitrogen containing material, whereby the disulfides are changed to the dithiocarbamic acids or free mercaptans. In the presence of metallic oxides, such as zinc oxide, mercaptans at once form the corresponding zinc salts; which may now be allowed to exert their rapid accelerating power without interfering with the factory processes, the latter having been completed.

Example idle-5, tetramethyl 'thiuram -disulfide-O.25.

This stock will not cure atL ordinary tembut after treatthen exposed to the atmosphere, air-curing ment with ammonia the stock will 0., while similar inthe use crease in curing power is "found by of dimethylamine vaporsorby painting the cold stock with tributylamine or aniline. j

these acids or time.

week, while (a) will amines or the like on treatment with to the dry. mixture,

I also find that,hydrogensulfide and like substances have the power of changing the disulfides to dithiocarbamic acids or mercaptans,'i whereby zinc salts are formed in the presence'of zinc oxide. Such materials may be .used in the place of an amine or ammonia in the example, with the precaution that excess of such gases be avoided as their ultimate action is to change all the metallic oxide in, the rubber mix to metallic sulfides.

I find twoprincipal advantages in the use of amines orammonia over the similar use of hydrpgensulfide or the like: 1. An excess of the amine or ammonia is not detrimental and there is therefore no danger of exposing the rubber mix totheir'action for too long a 2. The zinc dithiocarbamates or zinc mercaptides as formed from the disulfides by the action of ammonia or amines in the presence of zinc oxide have the power of combining withv still further quantitiesflif the vapors of ammonia or amine whereby their acceleratingpower is still further increased. This action is illustrated by the.

following example.

' Example 2.

A rubber mix is prepared according to the formula: rubber100, sulfur-4, zinc 0x- .1de,5, zinc dimethyl dithiocarbamate- 0.25. The mix is divided into two parts, one (a) being left untreated, while the other (6) is exposed to ammonia gas until-saturated and then allowed to stand in air until all odor of ammonialis lost. Portion (b) will air-cure at ordinary temperatures in one start to air-cure in about three weeks. .Portion (b) will cure in a hot air oven in twenty-five minutes at 80 C.. while (a) will still be undercured.

The zinc dithiocarbamatein Example 2 may be replaced by zinc salts of other thio acids such as mercaptabenzothiazole or dithiobenzoic acid wherein there exists a double bond adjacent to the group O-SH and increase of curingpower be obtained by ammonia or with an amine.

If the mix described in Example No. .2, be treated with hydrogen sulfide the acceleration is partially or wholly destroyed. for

low temperature cuungg which illustrates .the action of an exc s "ofhydrogen sulfide on the disulfides in Example N0. g l

The action of hydrogensulfide, ammonia, mixes (if rubber, sulfur, accelerator and metallic oxides is not limited as is shown by the following data. r

fi'wample 3.

rubber-400, zinc ox- A mix comprising,

tetramet hyl-thiuram ide5, sulfur-6 and disulfide-1 a cement by vent.

in 13 days or if treated with hydrogen sulfide for thirty seconds will gel in 24 hours. Extending-the time of ammoniav treatment increases the rate of cure while excess of hydrogen sulfide will entirely prevent gelation. The untreated cement will "stand for several months without vulcanization.

I do not limit myself to any definite; set of conditions during the exposure of the rub er mix to such ases, vapors orliquids as change the disulfides to dithiocarmabic acids or mercaptans. I may use increased pressure or temperature, and may effect vulcaniz'ation in the impregnating chamber by the application of heat during impregnation, by the use of such combination of time and temperature as would be insufficient to cause vulcanization by the amine or the organic disulfide when used separately. I may apply a liquid, such as aniline or methylene diamine, directly to the surface of the rubber mix and allow the same to penetrate the stock. After treat: ment, by the use of either a liquid or a gas, I may allow vulcanizationto take place at room temperature, or I mayspeed the cur ing process by vulcanizing in hot air or steam, with or without molds, or by other suitable procedure.

rga'nic monosulfides, bond in such a group as having a. double also come within the scope of my invention,

This cement, if treated with ammonia gas for twenty seconds Will gel or alr-cure acting with ammonia or amines to produce ultra accelerators of carbamic acids.

What I claim is:

the type of the dithio- 1. A method of effecting the vulcanization of a rubber mix containing the zinc salt of an oxygen-free organic acld, that comprises treating the mix with ammonia or with "an amine to 'amine additlon product of the zinc salt of the acid,'an'd produce therein the ammonia or vulcanizing the product.

2. A method of effecting the vulcanization of a rubbermix containing a zinc salt of a dithiocarbamic acid? that comprises treating the mix with the vapors of ammonia or of an amine to produce therein, the ammonia or amine addition product of the zinc dithiocarbamate, and vulcanizing the product.

3. A method of ,efi'ecting the vulcanization of a rubber mix containing zinc dimethyldi-- thiocarbamate which comprises producing in the rubber, by. treatment with the; vapor of ammonia or an amine, an ammonia or treating the cement with ammonia or with an amine addition'product of zinc dimethyl amine to produce therein the ammonia or dithiocarbamate. amine addition product of the zinc salt of 0 4. The method of effecting the ulcaniza' the acid, and vulcanizing the product. 5 lion of a rubber mix containing the zinc salt In witness whereof, I have hereunto signed of an oxygen-free organic acid, that commy name.

prises forming a cement of the mix, and CLAYTON BEDFORD. 

